calculations on a distillation process
The process involves the separation of a binary mixture containing heptane and ethylbenzene using a
countercurrently operated continuous fractionation unit. A feed at a flowrate of 252 mol/h containing 43
wt% heptane and 57 wt% ethyl benzene is to be fractionated at 1 bar to give a distillate with 95 mol%
heptane and a bottom product with 95 mol% ethyl benzene. The reflux ratio will be 70% more than the
minimum. The feed enthalpy of vaporization is 36825 J/mol and liquid heat capacity is 317 J/molK. In the
winter the temperature of the feed drops to 377 K while in the summer it reaches a maximum of 391 K.
i. Calculate the distillate and bottom product flowrates.
ii. Find the minimum number of stages.
iii. Find the number of actual trays needed for the design of the distillation column. Which
season will you design the unit for (winter or summer)? Explain.
iv. For the design case you chose, find the temperature of the top most tray, the reboiler and
the feed tray.
v. State the temperature requirement for the condenser.
vi. Find the compositions of the streams entering the feed stage.
vii. Calculate the recovery of heptane.
viii. If you are stuck with an existing column that has only 11 real trays, with the feed tray
being tray 5, what can you do to achieve the same distillate and bottom product
compositions? Explain with calculations/graph.